Studies of environmental conditions, climate, and their interactions have produced important new information relevant to Norse extinction in Greenland. Most revealing is the detailed evidence of climatic changes that occurred in the northwestern Atlantic beginning in the early 1300s. Changes in atmospheric temperature are recorded in such diverse materials as glacier ice derived from snow falling on the Greenland Ice Cap, fossil vegetation and pollen deposited annually in lake sediments, chemical signatures in isotopic composition of sea sediments, animal and human bones, and even the species of insect pests that accompanied Vikings and their animals as they settled new lands. These indicators clearly suggest that the climate was cooling in the 14th century, and that the Greenlandic environment had been depleted of its "natural capital"--its previously untapped grasslands and animal resources-over 500 years of farming practices in this delicate arctic climate.

Cores taken from the ocean bottom west of Iceland show evidence that the ocean conditions between the 8th and 12th centuries were relatively calm and that little sea ice was present to hinder navigation. The build-up of sea ice beginning in the 13th century correspond with evidence from ice cores whose layers of annual snowfall show isotopic evidence that the 14th century had the coldest climate known in Greenland during the past 700 years. Such conditions would have severely strained the farming resources of the Western Settlement and could well have caused its collapse.

Recently, analysis of ice-core samples has revealed them to be as sensitive to environmental change as tree rings. Seasonal variations in temperature and rainfall are indicated in the cores. Most environmental scientists believe it was not cold winters which were difficult for Norse farmers, but short summers. A series of short summers occurred in the late 1350s, just when the smaller Eastern Settlement went extinct. Farmers needed a long enough summer to grow sufficient hay to keep their animals alive through the early spring, when the Norse could then hunt ringed-seals on the ice. If the animals died before the seals arrived, the Norse could starve.

Cooling conditions are also registered in the remains of insects found on Norse farms. Lice and fleas differ depending on whether they live on humans or on animals. By the 12th century, lice remains in farms are of both human and animal types, indicating that the Norse conserved heat by keeping humans and animals together under one roof and enabling people to feed and care for animals during the long winter months. There are also two species of flies in Greenland, one adapted to warm temperatures, and the other adapted to colder temperatures which tell their own story. In early house remains, only evidence of the warm flies are found, but on 14th and 15th century farms, the cold climate fly is found in several rooms of the house.

Finally, fossil pollen indicate that the expansion of grasslands that
came with intensive grazing led to erosion. As nearby pastures degraded,
people sought to push production beyond the regenerative capacity of Greenland's fragile
landscape. This depleted the sustainable capabilities of the grasslands,
leading to lower and lower yields. Similar processes occurred in Iceland
and the Faeroes in the Middle Ages, resulting in decreased farm production and increased
reliance on the stock fish trade.

Climatic changes are not believed to be the sole cause of the extinction of the Norse, but it was likely the main stress on the remote Norse Greenlanders. Each bad winter and cool summer brought small farmers especially, into economic bondage, as they had to give up their stock and lands to wealthy, often absentee, landlords, or to the Church. The colonies may have slipped into a descending spiral in which the land's former "natural capital" was expended, never to return. At the edge of sustainable existence, there was no economic cushion to absorb even small problems such as the real or imagined threat of Inuit incursions, failure of social and economic reform, the appearance of pirates, etc.